In the production of semiconductor integrated circuits and other semiconductor articles from semiconductor wafers, it is often necessary to provide multiple metal layers on the wafer to serve as interconnect metallization which electrically connect the various devices on the integrated circuit to one another. Traditionally, aluminum has been used for such interconnects, however, it is now recognized that copper metallization may be preferable.
The semiconductor manufacturing industry has applied copper onto semiconductor wafers by using a “damascene” electroplating process where holes, commonly called “vias”, trenches or other recesses are formed onto a substrate and into which copper is filled. In the damascene process, the wafer is first provided with a metallic seed layer which is used to conduct electrical current during a subsequent metal electroplating step. The seed layer is a very thin layer of metal which can be applied using one or more of several processes. For example, the seed layer of metal can be laid down using physical vapor deposition or chemical vapor deposition processes to produce a layer on the order of 1,000 angstroms thick. The seed layer can advantageously be formed of copper, gold, nickel, palladium, or other metals. The seed layer is formed over a surface which is convoluted by the presence of the vias, trenches, or other recessed device features.
A copper layer is then electroplated onto the seed layer in the form of a blanket layer. The blanket layer is plated to an extent which forms an overlying layer, with the goal of providing a copper layer that fills the trenches and vias and extends a certain amount above these features. Such a blanket layer will typically be formed in thicknesses on the order of 10,000 to 15,000 angstroms (1–1.5 microns).
After the blanket layer has been electroplated onto the semiconductor wafer, excess metal material present outside of the vias, trenches, or other recesses is removed. The metal is removed to provide a resulting pattern of metal layer in the semiconductor integrated circuit being formed. The excess plated material can be removed, for example, using chemical mechanical planarization. Chemical mechanical planarization is a processing step which uses the combined action of a chemical removal agent and an abrasive which grinds and polishes the exposed metal surface to remove undesired parts of the metal layer applied in the electroplating step.
The electroplating of semiconductor wafers takes place in a reactor assembly. In such an assembly, an anode electrode is disposed in a plating bath, and the wafer with the seed layer thereon is used as a cathode. Commonly, only a lower face of the wafer contacts the surface of the plating bath. The wafer is held by a support system that also conducts the requisite cathode current to the wafer. The support system may comprise conductive fingers that secure the wafer in place and also contact the wafer in order to conduct electrical current for the plating operation.
One embodiment of a reactor assembly is disclosed in U.S. Pat. No. 5,985,126, entitled “Semiconductor Plating System Workpiece Support Having Workpiece-Engaging Electrodes With Distal Contact Part And Dielectric Cover,” which is herein incorporated by reference.
FIG. 1 illustrates such a reactor assembly 10 for electroplating a metal, such as copper, onto a semiconductor wafer. The assembly 10 includes a reactor vessel 11 and a processing or reactor head 12. The vessel includes an electroplating bowl assembly 14.
As shown in FIG. 1, the electroplating bowl assembly 14 includes a cup assembly 16 which is disposed within a reservoir chamber 18. Cup assembly 16 includes a fluid cup 20 holding the electroplating fluid for the electroplating process. The cup assembly of the illustrated embodiment also has a depending skirt 26 which extends below a cup bottom 30 and may have flutes open therethrough for fluid communication and release of any gas that might collect as the reservoir chamber fills with liquid. The cup can be made from polypropylene or other suitable material.
A bottom opening in the bottom wall 30 of the cup assembly 16 receives a polypropylene riser tube 34 which is adjustable in height relative thereto by a threaded connection between the bottom wall 30 and the tube 34. A fluid delivery tube 44 is disposed within the riser tube 34. A first end of the delivery tube 44 is secured by a threaded connection 45 to the rear portion of an anode shield 40 which carries an anode 42. The delivery tube 44 supports the anode within the cup. The fluid delivery tube 44 is secured to the riser tube 34 by a fitting 50. The fitting 50 can accommodate height adjustment of the delivery tube 44 within the riser tube. As such, the connection between the fitting 50 and the riser tube 34 facilitates vertical adjustment of the delivery tube and thus the anode vertical position. The delivery tube 44 can be made from a conductive material, such as titanium, and is used to conduct electrical current to the anode 42 as well as to supply electroplating fluid to the cup.
Electroplating fluid is provided to the cup through the delivery tube 44 and proceeds therefrom through fluid outlet openings 56. Electroplating fluid fills the cup through the openings 56, supplied from a electroplating fluid pump (not shown).
An upper edge of the cup side wall 60 forms a weir which limits the level of electroplating fluid or process fluid within the cup. This level is chosen so that only the bottom surface of the wafer W is contacted by the electroplating fluid. Excess fluid pours over this top edge into the reservoir chamber 18. The level of fluid in the chamber 18 can be maintained within a desired range for stability of operation by monitoring and controlling the fluid level with sensors and actuators. One configuration includes sensing a high level condition using an appropriate switch 63 and then draining fluid through a drain line controlled by a control valve (not shown). The out flow fluid from chamber 18 can be returned to a suitable reservoir. The fluid can then be treated with additional plating chemicals or other constituents of the plating or other process liquid, and used again.
A diffusion plate 66 is provided above the anode 42 for providing a more even distribution of the fluid plating bath across the surface of wafer W. Fluid passages in the form of perforations are provided over all, or a portion of, the diffusion plate 66 to allow fluid communication therethrough. The height of the diffusion plate within the cup assembly is adjustable using threaded diffusion plate height adjustment mechanisms 70.
The anode shield 40 is secured to the underside of the consumable anode 42 using anode shield fasteners 74. The anode shield prevents direct impingement on the anode by the plating solution as the solution passes into the processing chamber. The anode shield 40 and anode shield fasteners 74 can be made from a dielectric material, such as polyvinylidene fluoride or polypropylene. The anode shield serves to electrically isolate and physically protect the backside or the anode. It also reduces the consumption of organic plating fluid additives.
The processing head 12 holds a wafer W for rotation about a vertical axis R within the processing chamber. The processing head 12 includes a rotor assembly having a plurality of wafer-engaging fingers 89 that hold the wafer against holding features of the rotor. Fingers 89 are preferably adapted to conduct current between the wafer and a plating electrical power supply and act as current thieves. Portions of the processing head 12 may mate with the processing bowl assembly 14 to provide a substantially closed processing volume 13.
The processing head 12 can be supported by a head operator. The head operator can include an upper portion which is adjustable in elevation to allow height adjustment of the processing head. The head operator also can have a head connection shaft which is operable to pivot the head 12 about a horizontal pivot axis. Pivotal action of the processing head using the operator allows the processing head to be placed in an open or face-up position (not shown) for loading and unloading wafer W with a surface-to-be-processed in a face-up orientation.
Processing exhaust gas may be removed from the volume 13 through an exhaust system. FIG. 1 illustrates an outer vessel side wall 76 which extends upwardly from the vessel base plate 75 to a top end into which is nested an intermediate exhaust ring 77 having circumferentially spaced-apart slots 78 therethrough. The slots 78 communicate exhaust gas from inside the vessel 13 to a thin annular plenum 79 located between the intermediate exhaust ring 77 and the outer bowl side wall 76. Surrounding the outer bowl side wall 76 is a vessel ring assembly 80 which forms with the side wall 76 an external, annular collection chamber 81. Gas which is collected in the plenum 79 passes through intermittent orifices 82 and into the annular collection chamber 81. Gas collected in the collection chamber 81 is passed through an exhaust nozzle 83 to be collected and recycled.
The reactor assembly 10 of FIG. 1 can be used reliably in electroplating semiconductor wafers. However, the reactor head 12 is relatively expensive to manufacture. The reactor head 12 is adapted to move vertically, to rotate about a horizontal axis to facilitate loading and unloading wafers W, and to rotate about a vertical axis R to spin the wafer W during plating. Delivering electroplating power from an external power supply (not shown) to the fingers 89 of the reactor head 12 requires relatively complex, expensive electrical connections such as slip ring contacts. If the wafer W could be held stationary with respect to the electroplating bowl assembly 14, the reactor head 12 could be simplified by eliminating the motor used to rotate the wafer W about the axis R. The series of spaced-apart fingers 89 deliver adequate electroplating power to the wafer W. The relatively small contact area between the fingers 89 and the wafer can lead to localized variations in the electroplating power across the surface of the wafer, though, making it more difficulty to ensure good plating uniformity.